The present invention relates generally to white-light printers for use as a computer peripheral, and, more particularly, the invention relates to white-light printers for printing onto photosensitive media which use photosensors within the white-light printer to monitor light output of the white-light printer thus providing enhanced exposure control.
Electronic printers have long been used with computers to print images from the computers. To do so, the computer transmits an image as image data representative of the image to the printer through a common interface, and this image data, usually in digital form, is interpreted by the printer such that the image is printed on a hard copy medium. When a photographic print is desired, a white-light printer is generally used and the hard-copy medium is a photosensitive medium. The white-light printer then uses a modulated light source to scan image-bearing light across the photosensitive medium to create an image thereon.
Commonly, the modulated light source is a cathode ray tubes ("CRT") which is a fast, accurate, and easy to modulate light. A problem with using a CRT for this purpose is that as the CRT screen warms, the color of the light emitted from the CRT can change. Therefore, in order to get consistent exposures, the CRT must be fully warmed requiring that the printer be turned on for an extended period of time prior to making a first print.
Further, as the CRT ages the light output and color of the light continues to change. This results in precise factory calibration for light and color output of the CRT becoming useless over a period of time.
A further problem with using a CRT in a printer is that each CRT gives off a different amount of light, even with a constant voltage input. This problem has been addressed in factory calibration by intensity measurement and initial adjustment to ensure accuracy. This accuracy comes at the expense of increased manufacturing time and costs, and may not be stable over the life of the equipment.
To solve this problem, commercially available white-light printers have placed a photosensor within the white-light printer to monitor light intensity, or brightness, of the CRT light output. The results from the sensor are fed back to a processor which compensates the image signal from the computer for changes in brightness. While this method of compensation addresses the problem of varying brightness, it ignores changes in color of the white light.
Accordingly, it is an object of this invention to provide a white-light printer that automatically compensates for color changes in the white light.
It is another object of this invention to compensate for light intensity changes irrespective of a CRT used within a CRT-based white-light printer.
It is a further object of the invention to decrease manufacturing time by automatically calibrating each white-light printer without requiring mechanical adjustments.
These and other objects of the invention will be obvious and appear hereinafter.